1. Field of the Invention
The invention relates to use of low percents by weight of Cu in AlCu lines to improve functional yield by substantially reducing metal shorts for blanket metal deposition layers that are later subjected to reactive ion etching (RIE), when making microelectronic devices.
2. The Prior Art
Advances in interconnection technology have allowed continued improvements in integrated circuit density, performance and electrical characteristics, and this has led to a steady decline in the price per bit for dynamic random access memories (DRAMs).
In this connection, aluminum and aluminum alloys are used to form various electrical connections or wiring in electronic devices, such as integrated circuit structures. The aluminum or aluminum alloys are used to form the electrical connections between active and/or passive devices of the integrated circuit structures. For example, in fabricating a metallization structure, it has been the practice to use aluminum or an alloy thereof electrically connected to an underlying substrate, such as silicon. Although the aluminum and silicon are electrically connected together, the practice is to use intermediate electrically conducted layers interposed between the silicon and aluminum to provide better electrical connection to the silicon and to provide a physical barrier between the silicon and aluminum. This is for the purpose of preventing electromigration and spiking of the aluminum into the silicon, since migration of aluminum atoms into the underlying silicon can interfere with the performance and reliability of the resulting integrated circuit structure.
In addition to electromigration, the problem of hillock growth also occurs. These problems are especially pronounced at the submicron level. Further, as the demand increased for scaling down the dimensions of the interconnection lines and for increasing the current density, minimizing electromigration and hillock growth, improving functional yield was accomplished by alloying Cu in amounts of >2 weight-percent (wt %) to form AlCu lines. However, as the linewidth decreases, Cu defects become more critical to functional yield in AlCu RIE lines when performing blanket metal deposition followed by RIE when fabricating micro electronic devices—such that even when Cu is present in an amount of 0.5 wt %, excessive metal shorting occurs.
IBM Journal of Research and Development Vol. 39, No. 4, Jul. 19, 1995, pg. 4 disclose the use of AlCu alloy wiring innovation for enhancing reliability. Enhancing reliability included alleviating electromigration associated with AlSi metallurgy. Reliability is further enhanced by the use of thin layers of refractory metals, including the use of Ti, above and below the AlCu alloy layers. The refractory metals reduce contact resistance and provide an immobile redundant layer capable of shunting currents over small voids, thereby improving electromigration and stress-migration resistance.
A process of fabricating a metallization structure is disclosed in U.S. Pat. No. 5,943,601. The process comprises:                depositing onto a substrate a first layer of titanium having a thickness of about 90 to 110 angstroms; and then depositing a layer of aluminum and/or an aluminum alloy whereby the layer of aluminum and/or aluminum alloy is in electrical contact with the layer of the group IVA metal. The process of the present invention provides a metallization structure that exhibits enhanced electromigration characteristics along with being highly textured and being free of hillocks.        
The process may use AlCu.
U.S. Pat. No. 6,291,336 B1 disclose the use of AlCu metal deposition for robust RC via performance. The method deposits a metal layer on a semiconductor substrate, and comprises:
providing a silicon substrate having a first metal layer;
depositing an insulating layer over the metal layer;
forming via holes in the insulating layer;
performing a sputter etch cleaning of the via holes;
depositing a barrier layer in the via holes;
depositing a film of second metal over the barrier layer, wherein the second metal is aluminum copper alloy, wherein the second metal is deposited at a temperature between about 40° C. to 80° C., and wherein the thickness of the second metal is between about 6,000 to 6,600 Å; and
depositing an anti-reflective coating onto said film of metal.
L. A. Clevenger et al. in Interconnect Technology, 1999. IEEE International Conference, pgs. 29-31 disclose a process window for a Al(Cu) deposition temperature for a 0.2 /spl μ/m wide, 0.44 /spl μ/m pitch, Al RIE interconnection used in a 256 Mbit DRAM. While surface roughness and Al texture degrade slightly with increasing deposition temperature, other properties like RIE etchability, /spl Theta/-Al2Cu precipitate distribution and texture, sheet resistance and opens/shorts yield either improve or are unaffected as the Al deposition temperature is increased. All of these parameters combine to suggest a wide process window for Al deposition temperature for 0.2 /spl μ/m Al RIE interconnections.
T. Kwok in Reliability Physics Symposium 1988. 26th Annual Proceedings., International, pgs. 185-191 disclose the dependence of electromigration lifetime on the metal line geometry in Al—Cu of electromigration lifetime on the metal line geometry in Al—Cu submicron lines. The results indicated that as the linewidth decreases, the lifetime initially decreases and then increases below a crucial width. The lifetime also decreases with increasing film thickness. Those Al—Cu submicron lines with linewidth comparable to or smaller than film thickness have a longer electromigration lifetime than other Al—Cu fine lines. The effect of line length on electromigration lifetime was found to be small.
There is a need when utilizing AlCu metallization schemes for blanket metal deposition layers subjected to reactive ion etchings, to lessen or eliminate poor functional yield, poor process window and numerous Cu rich defects during microelectronic fabrication.